Of course they are genetically infused with an urge for human blood. To them healthy human blood tastes like an unimaginable sweet nectar beyond description. Beyond the pleasure any food brings a human. In addition some blood types are more favorable than others. Naturally the rarest blood types are the best tasting except for the rarest of all. AB- tastes bitter, and can in fact poison a vampire making them sick for a few hours. This is the blood type of vampire slayers who aren’t half-vampire. Only about 1% of the global populace has this blood type.

The best tasting blood is the next rarest which is B- of which 2% of the populace has flowing through their veins. Then next best is A-, O-, AB+, B+, A+, and O+ which is the most common human blood type on Earth. Vampires can get the aroma of these blood types through the air even 100 feet away from a human. In general they’ll pass over O+, and hold out for A+, and B+. So almost 40% of the populace doesn’t have to worry about being attacked by a vampire.